Objective: To examine the IFN-γ levels in patients with periodontitis and determine the difference in the levels of IFN-γ with the severity of the disease. Material and Methods: The study design was cross-sectional, and the sample consisted of 31 patients, aged between 18 and 64 years. Plaque index (PlI), calculus index (CI), and papillary bleeding index (PBI) were measured. Pocket depth (PD), recession, and clinical attachment loss (CAL) (mm) were measured at six sites per teeth. For mild/moderate periodontitis, pocket depth ≥4 mm in 1-3 sites was required, while the essential criteria for severe periodontitis were pocket depth ≥5 mm, clinical attachment loss >3 mm in more than 3 sites ≥2 quadrants. The IFN-γ levels were measured by performing enzyme-linked immunosorbent assay with the gingival crevicular fluid (GCF) samples. The measurements were made in two different sites, and the severity of periodontitis was categorized based on the pocket depth, attachment loss, and the remaining natural teeth. Kruskal-Wallis test, Mann-Whitney test, and Spearman's rank correlation coefficient were. Results: The levels of IFN-γ (pg/mL) were correlated with the severity of the periodontal status, with p <0.05. Clinical parameters of periodontitis also correlated with the level of IFN-γ (pg/mL). Conclusion: Subjects with periodontitis presented greater levels of IFN-γ (pg/mL) in GCF than the periodontal healthy individuals. This result showed the role of IFN-γ in the inflammation.